A winter storm is gripping the eastern US, dumping up to 16in (40cm) of snow in some areas, snarling up travel and cutting power supplies.
Incidents thought to be storm-related claimed five lives and forecasters warned of 35mph (56km/h) winds in what may be the worst snowstorm in a decade.
The 16in which fell at Reagan National Airport outside Washington was the most ever recorded on a single December day.
The storm system is moving north toward New York and Boston.
Parts of Connecticut, Rhode Island and Massachusetts could see more than 16in by Sunday night while as many as 10in may land on New York City, forecasters said.
Reagan airport was shut down for the night, most flights from Baltimore were cancelled and there were long delays for passengers using Philadelphia and New York.
Roads have been badly affected, too, with one transport official calling it a very serious storm.
As Washington's Union Station filled with travellers, some of them sprawled out on the floor, the passenger train service Amtrak said delays between Washington and Boston were averaging between 30 and 60 minutes.
At least two trains to Boston apparently departed more than four hours late.
Snow was being cleared from the M&T Bank Stadium in Baltimore ahead of an NFL game on Sunday
In Virginia, several hundred motorists became stranded in their vehicles and had to be rescued by the National Guard, using Humvees.
Some 500 people sought warmth and refuge in emergency shelters.
Three people died in the state. One was killed when a car hit a tree, a second died of exposure and a third was also apparently killed in a road traffic accident. In Ohio, two people were killed in accidents on snow-covered roads hit by the same storm system.
The US National Weather Service warned that weather conditions in the Washington area had made travel "extremely treacherous".
"Do not travel," it warned drivers.
"If you must travel, have a winter survival kit with you. If you get stranded, stay with your vehicle."
Washington Mayor Adrian Fenty asked residents to sit out the weekend snowstorm at home where possible.
US President Barack Obama, arriving back at Andrews Air Force Base in Virginia from the Copenhagen climate conference, travelled into Washington by motorcade rather than helicopter because of the weather.
Send us your comments Those who did venture out were treated to nearly desolate stores on what is usually one of the busiest shopping days of the year, The Associated Press reports.
In snow-bound areas, there were virtually no queues to get a picture with a mall Santa on the last weekend before Christmas, it adds.
"It's nice because no one's here," said shopper Nnika White, out buying a drum set for her boy of two in Richmond, Virginia.
"For shopping, it's great, but the roads are very, very bad," she added.
In New York, Mayor Michael Bloomberg said: "Hopefully, we'll have a little bit of a white Christmas."
The storm system originated over the Gulf of Mexico, unleashing flash floods in much of the US south-east.
The rain turned to snow as the storm tracked north-eastward into sub-freezing temperatures.